Astrophys. J., 871, 247-247 (2019/February-1)
The origin of r-process enhanced metal-poor halo stars in now-destroyed ultra-faint dwarf galaxies.
BRAUER K., JI A.P., FREBEL A., DOOLEY G.A., GOMEZ F.A. and O'SHEA B.W.
Abstract (from CDS):
The highly r-process-enhanced (r-II) metal-poor halo stars we observe today could play a key role in understanding early ultra-faint dwarf galaxies (UFDs), the smallest building blocks of the Milky Way. If a significant fraction of metal-poor r-II halo stars originated in the UFDs that merged to help form the Milky Way, observations of r-II stars could help us study these now-destroyed systems and probe the formation history of our Galaxy. To conduct our initial investigation into this possible connection, we use high-resolution cosmological simulations of Milky Way-mass galaxies from the Caterpillar suite in combination with a simple, empirically motivated treatment of r-process enrichment. We determine the fraction of metal-poor halo stars that could have formed from highly r-process-enhanced gas in now-destroyed low-mass UFDs, the simulated r-II fraction, and compare it to the "as observed" r-II fraction. We find that the simulated fraction, fr–II,sim ∼ 1%-2%, can account for around half of the "as observed" fraction, fr–II,obs ∼ 2%-4%. The "as observed" fraction likely overrepresents the fraction of r-II stars due to incomplete sampling, though, meaning fr–II,sim likely accounts for more than half of the true fr–II,obs. Further considering some parameter variations and scatter between individual simulations, the simulated fraction can account for around 20%-80% of the "as observed" fraction.
© 2019. The American Astronomical Society. All rights reserved.
galaxies: dwarf - Galaxy: formation - Galaxy: halo - nuclear reactions, nucleosynthesis, abundances
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